The present invention relates to visualization of medical devices within a body generally and, more particularly, to visualization by means of ultrasound imaging of implantable cardiac pacing or defibrillation leads equipped with guiding stylets, guidewires, needles, or other guiding devices.
Cardiac pacing and defibrillation leads are generally placed under fluoroscopic observation, allowing the physician to follow the lead as it is passed through the venous system into the heart. However, as fluoroscopes are extremely expensive, a less costly method of visualization of cardiac pacing and defibrillation leads would be desirable. Additionally, it would be advantageous to use the guiding mechanisms as delivered without modification of any sort. One alternative mechanism for visualization of pacing leads placed within the body involves the use of an ultrasonic transducer located in the distal end of a stylet that is coupled to a vibrator connected to the proximal end of the stylet. In U.S. Pat. No. 5,968,085 issued to Morris and Lipson, incorporated herein by reference in its entirety, the use of an ultrasonic transducer coupled to a stylet or guidewire to facilitate the display of the lead position within the body on external ultrasound equipment is disclosed. Other examples of such visualization and localization systems are disclosed in U.S. Pat. No. 5,421,336 issued to DeBernardis, U.S. Pat. No. 5,161,536 issued to Vilkomerson et al, and in U.S. Pat. No. 4,697,595 issued to Breyer et al., all incorporated herein by reference in their entireties. In particular, U.S. Pat. No. 5,343,865 to Gardineer et al. discloses a system that uses a rigid coupling mechanism to transfer vibrations to a needle or cannula. The vibrations may be transferred in the X, Y, and Z planes.
One problem with transferring vibrations to a longer, flexible structure such as a lead body involves the difficulty in transferring vibrations around bends in the leads occurring during lead placement within the venous system. In practice, it has been found that transverse waves applied to a stylet inserted into a pacing lead are generally not transmitted around the bends typical of a lead used in clinical practice. In the region of a bend, the stylet is forced against the wall of the lead lumen. Friction with the lead wall dampens the vibrations so that a color Doppler image cannot be obtained beyond the bend. Similarly, pinching the lead eliminates the Doppler image beyond the pinch point.
What is needed, therefore, is an improved system that can be adapted for transferring vibrations down an elongated, flexible structure such as a lead body so that a color Doppler image can be generated to indicate lead location.
The present invention is directed to an improved visualization of cardiac pacing or defibrillation leads used in conjunction with an unmodified stylet or guidewire that is inserted through a vibrator. This present invention accomplishes this enhancement by means of a piezoelectric activator by which the user can vary the sweep frequency of the vibration to enhance the visualization of various portions of the lead (e.g., the lead tip as well as the fixation tines) on a color Doppler ultrasound system. This invention enhances the Doppler images of pacemaker and defibrillator leads and catheters that are equipped with guidewires, stylets, or needles, and provides images that cannot normally be visualized via conventional ultrasound equipment. The piezoelectric activator produces linear, i.e., longitudinal, vibrations throughout the stylet, that are then transferred to the pacing lead. These vibrations enhance the Doppler image of the whole lead or catheter as well as the lead tip, which cannot normally be imaged via conventional ultrasound equipment. A stylet is advanced through the piezoelectric activator via a modified stylet guide, through a curved piece of hypodermic tubing (hypo tube) coupled to a vibrating diaphragm, then through a standard stylet guide, and into the proximal entry orifice of the lead connector pin. When the vibrating diaphragm is driven by an oscillatory signal, the hypo tube rubs against the stylet thereby transferring the vibration to the stylet. When united to the lead or catheter, the stylet may be used in the conventional manner to assist passage of the lead or catheter through the venous system to gain access to the superior vena cava and, from there, to the chamber(s) of the heart. Throughout this passage, the operator may apply varying vibration frequencies to the stylet to allow visualization of the lead or catheter position at various critical points.
The present invention is adapted to allow longitudinal waves to be transferred along the length of the stylet without being dampened by friction between the stylet and the lead lumen. Friction between the curved hypo tube and the stylet transfers energy from the vibrating diaphragm to the stylet. Because the stylet is an incompressible body, longitudinal vibrations introduced at the proximal end of the stylet are transmitted to the distal end of the stylet. Friction between the stylet and the lead lumen wall transfers some of the vibrational energy to the lead body wherever the stylet makes contact with the lead body. As a result, waves may be transferred around bends and kinks in the lead. A component of this energy is converted to radial vibrations that make the entire course of the lead body visible on Doppler ultrasound.
The current invention is adapted for use with any ordinary, unmodified, stylet or other guiding device. For example, the stylet insertion pin is anchored to the vibrating diaphragm via a friction fit provided by the curved hypo tube. The hypo tube thereby acts as a short extension of the lead or catheter, and freely admits any conventional stylet, guidewire, or other guiding device acceptable for use with the selected lead. The tubing that transfers vibrational energy to the stylet is sized to allow a sliding fit for any stylet that may be used with a selected lead. The dynamic performance of the stylet as used in conjunction with the current invention is not significantly different from the performance of the stylet as used without the inventive system. Moreover, because the stylet is not an integral part of the vibrating mechanism, any disposable stylet may be employed with the system, whereas the remainder of the system is not disposable.